This invention relates generally to email, and more specifically to minimizing the amount of spam traffic transported over an email system.
More than 75% of all email traffic on the internet is spam. To date, spam-blocking efforts have taken two main approaches: (1) content-based filtering and (2) IP-based blacklisting. Both of these techniques are losing their potency as spammers become more agile. Spammers evade IP-based blacklists with nimble use of the IP address space such as stealing IP addresses on the same local network. Dynamically assigned IP addresses together with virtually untraceable URL's make it increasingly more difficult to limit spam traffic. For example, services such as www.tinyurl.com take an input URL and create multiple alias URL's by hashing the input URL. The generated hash URL's all take a user back to the original site specified by the input URL. When a hashed URL is used to create an email or other account, it is very difficult to trace back as numerous hash functions can be used to create a diverse selection of URL's on the fly.
To make matters worse, as most spam is now being launched by bots, spammers can send a large volume of spam in aggregate while only sending a small volume of spam to any single domain from a given IP address. The “low” and “slow” spam sending pattern and the ease with which spammers can quickly change the IP addresses from which they are sending spam has rendered today's methods of blacklisting spamming IP addresses less effective than they once were.